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RNGCryptoServiceProvider.GetBytes Method

Fills an array of bytes with a cryptographically strong sequence of random values.

Namespace:  System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Overrides Sub GetBytes ( _
	data As Byte() _
)

Parameters

data
Type: System.Byte()

The array to fill with a cryptographically strong sequence of random values.

ExceptionCondition
CryptographicException

The cryptographic service provider (CSP) cannot be acquired.

ArgumentNullException

data is Nothing.

The length of the byte array determines how many cryptographically strong random bytes are produced.

This method is thread safe.

The following code example shows how to create a random number with the RNGCryptoServiceProvider class.

'The following sample uses the Cryptography class to simulate the roll of a dice. 
Imports System
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography



Class RNGCSP
    Private Shared rngCsp As New RNGCryptoServiceProvider()
    ' Main method. 
    Public Shared Sub Main()
        Const totalRolls As Integer = 25000
        Dim results(5) As Integer 

        ' Roll the dice 25000 times and display 
        ' the results to the console. 
        Dim x As Integer 
        For x = 0 To totalRolls
            Dim roll As Byte = RollDice(System.Convert.ToByte(results.Length))
            results((roll - 1)) += 1
        Next x
        Dim i As Integer 

        While i < results.Length
            Console.WriteLine("{0}: {1} ({2:p1})", i + 1, results(i), System.Convert.ToDouble(results(i)) / System.Convert.ToDouble(totalRolls))
            i += 1
        End While
        rngCsp.Dispose()
        Console.ReadLine()
    End Sub 


    ' This method simulates a roll of the dice. The input parameter is the 
    ' number of sides of the dice. 
    Public Shared Function RollDice(ByVal numberSides As Byte) As Byte 
        If numberSides <= 0 Then 
            Throw New ArgumentOutOfRangeException("NumSides")
        End If  
        ' Create a byte array to hold the random value. 
        Dim randomNumber(0) As Byte 
        Do 
            ' Fill the array with a random value.
            rngCsp.GetBytes(randomNumber)
        Loop While Not IsFairRoll(randomNumber(0), numberSides)
        ' Return the random number mod the number 
        ' of sides.  The possible values are zero- 
        ' based, so we add one. 
        Return System.Convert.ToByte(randomNumber(0) Mod numberSides + 1)

    End Function 


    Private Shared Function IsFairRoll(ByVal roll As Byte, ByVal numSides As Byte) As Boolean 
        ' There are MaxValue / numSides full sets of numbers that can come up 
        ' in a single byte.  For instance, if we have a 6 sided die, there are 
        ' 42 full sets of 1-6 that come up.  The 43rd set is incomplete. 
        Dim fullSetsOfValues As Integer = [Byte].MaxValue / numSides

        ' If the roll is within this range of fair values, then we let it continue. 
        ' In the 6 sided die case, a roll between 0 and 251 is allowed.  (We use 
        ' < rather than <= since the = portion allows through an extra 0 value). 
        ' 252 through 255 would provide an extra 0, 1, 2, 3 so they are not fair 
        ' to use. 
        Return roll < numSides * fullSetsOfValues

    End Function 'IsFairRoll
End Class

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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